Prof. Dr. D. Schröder Page 1

GIS in Hydrology and Water Management - ENWAT

Tutorial: Introduction to ArcGIS Training Objectives

Present hydrological relevant data in thematic maps ,prepare data for further hydrological analysis, perform simple spatial analysis related to hydrology and water resource management:

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To get acquaintance with the user interface of ArcGIS Understand the philosophy of GIS Learn how to integrate and manage spatial data Learn how to design thematic maps Perform analysis on vector data Build a topological database and perform simple topological analysis Interpolate raster Learn how to design common GIS analysis workflows

Given Datasets: Different data layers for the Watershed of river Rems, a tributary of the river Neckar, are given, including • Land cover (Corine Land Cover dataset) • Location (location of places in the state of Baden-Württemberg) • Soil (from the Waboa dataset) • Groundwater monitoring stations (from the WaBoa dataset) •

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River Rems (from the WaBoa dataset) DEM (DGM50 from BGK) Watershed boundary and sub catchments (derived from DEM) Orthophoto Cadastral data (land parcel boundaries and building outlines from the ALK) Digital landscape model (ATKIS-DLM25) Climate data Some auxiliary data

Remark: All the functionality explained in this tutorial is based on ArcGIS 9.2! If you are using an older version, may be the workflow will be slightly different. Task 1: Map of land cover of the Rems watershed

To introduce the basics of ArcGIS we will start in designing a first map. The map should show in appropriate symbology the land cover, the watershed of river Rems as well as the river network. According to their importance, the tributaries of river Rems should be mapped in different width. Finally, we want to add map marginals (meta data of the map) like scale bar, legend, coordinate system information and so forth.

There are twoArcGIS desktop applications: • ArcCatalog and •

ArcMap

ArcCatalog is the application for managing the spatial data, for managing the database design, and for recording and viewing metadata. ArcMap is used for all mapping and editing tasks, as well as for map-based analysis, for data conversion and geoprocessing. Using these two

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applications together, you can perform any GIS task, simple to advanced, including mapping, data management, geographic analysis, data editing, and geoprocessing. The ArcGIS desktop applications can be accessed using three software products, each providing a higher level of functionality: • ArcView provides comprehensive mapping and analysis tools, along with simple editing and geoprocessing tools. • ArcEditor includes the full functionality of ArcView, with the addition of advanced editing capabilities. • ArcInfo extends the functionality of both to include advanced geoprocessing. Main difference is the functionality of the so called ArcToolbox . The complete ArcToolbox comes only with ArcInfo, a lighter version comes with ArcView and ArcEditor. ArcToolbox for ArcInfo comes with a complete, comprehensive set of tools (well over 150) for geoprocessing, data conversion, map sheet management, overlay analysis, map projection, and much more. ArcToolbox for ArcView and ArcEditor contains more than 20 commonly used tools for data conversion and management. The main task of ArcMap is to visualize spatial related data. The data in ArcMap is organized as maps. ArcMap stores a map as a map document (a file with the extension *.mxd) so you can redisplay it, modify it, or share it with other ArcMap users. The map document doesn’t store the actual data, but rather references the data stored on disk along with information about how it should be displayed. The map document also stores other information about the map such as its size and the map elements (title, scale bar, and so on). Geographic information is displayed on a map as layers; each layer represents a particular type of feature such as streams, lakes, or highways. A layer can only hold one type of geometry, i.e. points, lines, areas, images, or grids. The geometry type of a layer is shown in the table of contents. Layers are listed in the ArcMap table of contents and can be further organized into data frames. A data frame simply groups, in a separate frame, the layers that you want to display together, i.e. all layers in one data frame can be visualized on one map. add layers

ArcCatalog

ArcToolbox

MapWindow

Tools icon bar

data frame point layer line layer area layer table of content

1. Start ArcMap with a new map. 2. Prepare the data frame by setting the output coordinate system and the map units (right mouse click o the data frame in the TOC -> properties. Use the predefined projected national grid DHDN 3 Degree Gauss Zone 3). Set the reference scale (which will be used for annotations) to 1:200 000. 3. Load the shape-file CLC_Rems.shp (Corine land cover), location_BW.shp, river Rems.shp and Neckar.shp into the map.

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Hint: if you access several datasets located in the same folder, you should use Connect to Folder in the Add Data dialog. The order in which the layers are listed in the TOC is also important. The layers at the top of the TOC are drawn on top of those below it. You can change the order by drag & drop the layer's title in the display tab of the TOC. 5. Load the shape file RemsWatershed.shp. 6. Change the display order of the different layers. (Hint: Make always sure that area layers are at the bottom of the list in the table of content, otherwise they may cover point and line layers. To see “through” one area layer, you should set the symbology and the transparency appropriate; just click on the colored symbol in the TOC for the specific layer and select one of the predefined fill patterns. For the transparency use the Display tab of the property dialog of the specific layer)

There are several different buttons and tools in the tools menu for moving around a map (a button has to be clicked each time you want to repeat the action, a tool stays selected until you unselect the action): • zoom in/zoom out (either by clicking into the map with a fixed extent or by drawing a box in the map) • zoom to previous/next extent • pan • zoom to full extent • zoom to layer (select the layer in the TOC and use the right button on the mouse) • zoom to selected feature (to select a feature choose the Select Element-button and click on the feature or draw a box around it) 7. Test the different tools! (Hint: if the icons are not available, use Tools ->Customize … to add them to your user interface or right mouse click in some empty space of the tool bar area to see the list of all available tool bars)

To get a nicer layout of our map we want to label some rivers and locations, give a title to the map and change the displaying style of some features. 8. The meaning of the different land cover codes are given in a database table. Load the data base table clc_code to your view. You can now join your land cover layer with the codes from the database. (Right mouse click on the layer in the TOC -> join). To each land cover polygon the description for the specific code of this polygon will be added in its attribute table temporarily. 9. After joining, you can use the joined attributes to create a thematic map, i.e. to change the symbology so it is determined by the value of the attribute description. Use a meaningful symbology for each of the different land cover classes. 10. Save the land cover as a new layer, so we can reuse the defined symbology in other projects using Save to layer from the context menu of the layer.

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Another possibility for mapping an attribute value is to change the size or width of a symbol or line. 11. The attribute table of the river Rems contains the attribute GKZ_Stufe, which is the level of the stream code (Gewässerkennzeichen). Use the level to show the river network in different line width.

Labeling is the process of placing a descriptive text string next to one or more features on your map. Labels help a map reader to interpret a map. How you label your maps depends on the type of data you’re displaying, what features you want to label, and how you’ll ultimately use the map. In ArcMap you have to distinguish between labels and annotation. Labels are placed dynamically and the displayed value is derived from an attribute of the features, whereas annotations are texts which are no longer linked to the original features (except you link it explicitly to the feature). To display labels for a layer, you simply specify what attribute of the features you want to label and then turn labeling on (double click on the layer entry you want to label in the TOC and select the label tab). ArcMap dynamically places labels on or near the features they describe. You can also control the font, size, and color of the text to help differentiate labels for different types of features. As you pan and zoom around your map, ArcMap dynamically adjusts the labels to fit the available space. At smaller scales, you see fewer labels because ArcMap has less space to place them. Because fewer features can be labeled, you might want to prioritize the labeling of some features. For each layer you want to label, you can set its labeling priority. This

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means that a feature in a layer with a higher priority will be labeled over a feature in another layer with a lower priority. Similarly, within a single layer you can set labeling priorities on specific groups of features. When you need more precise control over label placement, you can convert the dynamic labels to annotation. Converting labels to annotation allows you to manually control the labeling of features. The conversion process creates text graphics from the dynamic labels and displays them on your map. Then you can work with each label, or text graphic, independently 12. Double click on the Rems layer in the TOC. Click on the label tab and select the attribute FL_name as Label Field. Repeat the steps for the location layer. Use different font, color, and size for the labels of the different layers. Now zoom in and out! 13. To control the priority of the labels use the Placement Properties dialog.

When you convert the labels to annotation, you can store them with the map as an annotation group, or you can store them separately in a geodatabase as an annotation feature class and reference it like other data on your map. Storing annotation in a geodatabase is similar to storing geographic features - line, point, and polygon - in a geodatabase. You can add annotation stored in a geodatabase to any map. It appears as an annotation layer in the table of contents. Labels stored as an annotation group in the map document will be deleted as you delete the map. Remark: For storing annotation in a database, i.e. an Access mdb-file, the database has to exist. To create a new one, you have to use ArcCatalog. Some additional settings as the specification of the coordinate system and the precision of the coordinates are necessary. Stored annotations in a database are handled as text layers, i.e. can they can only be changed using the edit tools as for point, line or area layers. 14. Use Convert Labels to Annotation (right mouse click on the layer) to store the labels shown in your actual extent and store them in the map. You can now move the labels where you like. To move a label, click the Select Element tool from the Drawing bar and click on the label you want to move. To change the layout of the selected label, use the property dialog (right mouse click on the selected label) 15. Add a title to your map using the New text tool from the drawing bar. The text can be moved and resized in the same way as labels.

Remark: Both the annotations stored in the map as well as the title are graphic elements and not geographic features. Thus they have to be manipulated differently than features! If you are satisfied with your map layout, you can start to prepare the map for final printing: 16. From the View menu, choose Layout View. In the Layout View you can arrange the final layout for your map. Most important of course is the data frame, showing your geographic information. In addition to a data frame, most maps contain one or more other map elements. These include titles, North arrows, legends, scale bars, scale text, graphs, reports, text labels, and graphics. One challenge of cartography is to arrange the elements of the map on the page to create a useful, visually pleasing map. You can add these elements manually (use the Insert menu) or you can use predefined templates (use Change Layout from the Layout tool bar). 17. By clicking on an object in the layout view, you can change some properties of the layout, e.g. the scale, the properties of the scale bar, the north arrow, etc. The contents can not be changed here. By default, ArcMap maintains a live link between the layout view and the data view. This means that changes you make to the data view are immediately reflected in the layout.

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Hint: you can add a second map, e.g. an overview map by adding a new data frame to the TOC and design this map again in the Data View. Remember, only one data frame can be the active one! Some properties important for the final layout are only accessible by the property dialog of the data frame, e.g. grid and graticules. After you have finished preparing the layout, you can print your map (use the print preview to check the final layout) as usual. Before leaving your work, you don’t forget to save your work! Make sure that you have selected the right folder!

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Task 2: Diagram map of the land cover balance for the Rems catchments

In the following task, a more complex workflow is shown. The aim is to create a diagram map, i.e. a map showing on a pie chart the share of each land cover in a geographical unit. Before we start, some hints for improving an interactive map are given. Usually, to each geographical feature additional attributes are linked. The advantage of a digital “interactive” map is, that the information about these attributes can be retrieved. To see the attributes for an individual feature you have just to point to them. (Click the Identify button on the Tools bar, than click the mouse pointer over the map feature you want to identify. The features in all visible layers under the pointer will be identified.) One of the feature attributes can be used as a map tip. To define a map tip, here are the steps you have to do: In the table of contents, right-click the layer for which you want to display map tips and click Properties. Click the Display tab and check Show Map Tips. Click the Fields tab. Click the Primary Display Field dropdown arrow and click the attribute field you want to display as the map tip. Click OK. Move the mouse pointer over a feature to see the map tip. The attributes belonging to the geometric features of a shape-File are stored in a dBase-file with the extension dbf. The data to a layer can be shown in a (database) table (context menu of layer Open Attribute Table). The layer in a map view and the corresponding table are linked, i.e. if you select a feature in your map the corresponding entry in the table is highlighted and vice versa. Of course you can select more than one feature or record by using the ctrl-key. A theme's attribute table can often contain a lot of fields. By rearranging, hiding, or renaming the fields, you can control exactly how the table appears on screen. Use the Fields tab of the layer property dialog to customize the table view. By sorting an attribute table you can list the currently selected features on your map in order of importance. Select a column and use the context menu. To change data in a table (and in a map view) you have first to activate the edit mode (Editor -> Start Editing). In this mode you can change a single value, add columns, etc. In new additional columns you can store for instance some calculated data. For simple editing, you have to use the edit-icon.

Now we are prepared to arrange our data to design the new map, which should visualize the share of the different land covers of the sub catchments of the Rems watershed as pie diagrams. The balance should include the three classes settlement, farmland and forest. 1. Load the catchments shape file (remark: the catchments have been created using the Spatial Analyst and a DEM with resolution 1" x 1" (ca. 30m × 20m in GK projection). 2. Select the catchments inside the Rems watershed using Select by location. The different operators which can be used for this selection will be discussed in the lecture, here just use the most general one which is intersect (select all the catchments which interacts with the geometry of the watershed, i.e. which fall inside the watershed). 3. Create a new layer from the selected (right mouse click on the layer in the TOC -> Selection. Remark: The layer will not contain any data physically! If you need a real data set of your selected features, use Data -> Data Export).

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Next we have to intersect the new catchment layer with the land cover layer. An intersection is a more complicated tool, as it will calculate new geometries, which will take some time (Hint: For that reason you should restrict the data sets to be intersected as much as possible e.g. using Selection by Attribute or Selection by Location). The result of the intersection is a new polygon shape file with a polygon for each land cover in each catchment. 4. Use the Intersection tool from the ArcToolbox. As Input layers select the two layers to intersect. As result, a new Shape-file will be created. (Hint: be careful about the location where the new file will be stored. Rename it to give a more meaningful name to it)

As we want to have our evaluation for each catchment, we will dissolve the new geometries using the catchment ID and the different land covers. Dissolve will aggregate features based on specified attributes. So all geometries of a specific catchment with the same land cover will be combined to one feature. 5. Use the Dissolve tool from the ArcToolbox. As Input layer select the intersection layer from the step before. As dissolve fields use the Catch_ID which identifies the different catchments and the code2000 which identifies the land cover in the year of the evaluation. As result, a new Shape-file will be created.

In the next step, we will calculate the size of the areas for the different land covers in each catchment. To store these values, new fields have to be added to the attribute table and then they have to be populated by the respective values. This manipulation can be done using the Field calculator. For simple calculations the syntax is straight forward, for more sophisticated VBA (Visual Basic for Application), the included macro programming language, has to be used. Before performing the calculation, you have to select those features for which you want to carry out the calculation. The Selection by Attributes tool from the user interface can be used, which allows you to define SQL like queries as working within a data base.

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6. Open the attribute table for your dissolved features. Use Options -> Add field to add the field area_urban. The calculated values will be floating point numbers, thus use float or double as Type. 7. Repeat this step for the other two fields area_farm and area_forest. 8. Define a Selection by Attributes… query to select all settlement features, i.e. all the features with clc code between 100 and 199. The selected features will be highlighted on the map and in the attribute table. 9. Check that the correct features are highlighted in the table. Select the column you want to populate in the table, which is the area_urban. Right mouse click and use Calculate geometry. 10. Repeat the steps 7 to 8 for the other two columns.

Now we can use the dissolve tool again to get only one feature for each catchment with the three new columns. To keep the columns, you have to define what should happen to the values in the aggregation. 11. Use again the Dissolve tool, Use the catch_ID as Dissolve field. Add the three area columns as Statistic Fields and define as Statistic Type e.g. SUM (remark: here the type doesn’t matter, as we have only one value in each column for each catchment)

12. Now we are ready to create the diagram map. In the symbology dialog for the layer select Charts to specify the settings for a diagram map.

The whole workflow is an example for a rather complex analysis and managing process. If you have to repeat it, it would be rather time consuming and boring. Thus it is a good idea to store the whole workflow as a script using the model builder. The process chain for the whole workflow is given below.

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Task 3: Create buffers along rivers

Rivers are generally modeled as linear features, but there are issues that may involve characteristics of the land near the rivers. Simple constant “buffer” might be needed to access the river maintenance, but for protecting a river against non-point source pollution the width of a buffer will be related to the land cover type. In this tutorial we will use as starting data with the land cover as a polygon feature class and the river network as linear features. We are supposed to create a buffer along the rivers whose width depends on the current land cover near the river.

We start with loading our data to a new project. 3. Load the two shape files Rems.shp and CLC_Rems.shp with the clc codes from the database table to a new project in ArcMap. 4. Join the codes to the land cover layer. 5. Import the symbology for the land cover from the layer file you have saved in the project before.

The river reaches from the river Rems layer generally pass several different types of land cover. On the other hand, one land cover polygon may contain several river reaches. Thus we have a many-to-many relationship between river reaches and land cover polygons. Thus in the following step, we have to break this n:n relationship into 1:n relationships. The geometry of our river reaches has to be split, when a new land cover type is reached. This is done by an intersection of the rivers and the land cover polygons. In addition, in performing the intersection, the attributes of the corresponding land cover polygon will be added to the specific new generated river segment. 4. Intersect the Rems layer and the land cover layer. A new shape file will be created. 5. Check geometry type and the attribute table of the new created layer. It should be still line including as attribute the land cover description as well as the values for your buffer zones to be created.

In the next step the buffer zones will be created. They will be based on the field buffer , i.e. each buffer will have a different width depending on the value stored in the field. 7. Use the Buffer tool from ArcToolbox. Use the intersection result as input, as Distance the buffer field, Side Full which means a buffer on both sides, End Type Round, and Dissolve Type All which means only one multipart feature will be created. 8. To check visual the result, set the transparency of the layer e.g. to 30% (Properties…-> Display)

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Task 4: Assign site properties to monitoring points (spatial join)

To manage monitoring points site characteristics like the surrounding land cover, distance to the nearest river, surrounding land cover and others are important. In this tutorial we will join this information to the attribute table of the monitoring points.

First, we will assign the land cover layer attributes to our monitoring stations using a spatial join. Remark: Check carefully the settings for the coordinate systems of your layers. If they don’t fit, the spatial join will be rejected or give wrong results. If there is no information about the coordinate system specified, use ArcCatalog to set the proper information. 1. Load the groundwater_monitoring shape file to your project. 2. Join the attributes of the land cover layer to the points using a spatial join. The

The result can for instance be used to detect all monitoring points where the surrounding land cover 2000 is different from that of 1990. 3. Use a Selection by Attributes to detect the monitoring points with different land cover for 1990 and 2000.

Next we have to assign the distance from the nearest river to each monitoring point, which is just another spatial join. The join dialog will look different depending on the geometry types of the features which will be involved. 4. Join the Rems layer file to the monitoring

points using a spatial join. Check the settings in the dialog box carefully. The results will be written to a new shape file. 5. Check the result by using different sizes for the symbols depending on the distance which have been calculated.

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Task 5: Defining and tracing a topological network For doing tracing in a network, first a topological correct network has to be build. Prerequisite of a geometrical network in ArcGIS are geometrically correct river segments, i.e. a segment runs from a source to the next junction, from junction to junction, or from junction to the outlet (sink). In the map below each segment is shown by a different color and number. More sophisticated hydrological tools like ArcHydro are based on geometric networks.

The topological information of a network, i.e. the edges and junctions as feature classes and their relationships, will be handled in ArcGIS by database tables. Here a Personal Geodatabase will be used, which is an Access database file. Inside a geo database, the feature classes are organized as data sets. A data set is a set of feature classes with common characteristics, like coordinate system, extent, etc. The data management in the first steps will be done using ArcCatalog. 1. Create a new Personal Geodatabase. Call it Rems. 2. Inside the database create a new data set. Call it Rems. Assign as coordinate system DHDN_3_Degree_Gauss_Zone_3. 3. Import the Rems shape file to the data set. Call the new feature class Rems.

To create a complex network, which is a net with an outlet and defined flow directions, we need the junctions as a separate point layer. As it doesn’t exist, we have first to create a simple network, just to extract the junctions. 4. From the context menu of the data set Rems start the Build Geometric Network wizard by clicking New -> Geometric Network. 5. Follow the wizard using existing features, layer Rems on which you want to base your network, NO complex edges, YES to snap the edges and junctions, NO weights. (Hint: if the first run for building the network fails, remove the zombie net, and start a second time using NO for preserving enable settings). The (simple) net topology as well as a new layer with the junctions has been created. 6. Export the new junction layer to a shape file. 7. Delete your simple network layer, as we will now create a complex network.

In the next steps, a complex network will be build. A complex network includes at least one sink, so that the flow direction can be determined. 8. Import the junctions you have created to the data set. Call it Rems_Junction. 9. Use again the Build Geometric Network wizard with the following settings: using existing features, Rems and Rems_Junction as feature on which you want to build your network, No enable all network features, YES for building complex edges, No for snapping, YES for sinks and sources, No for weights.

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After creating our network, we will analyse it using ArcMap. First we have to set the sink, i.e. the outlet point, and the flow directions for each segment. 10. 11.

12.

13.

Start ArcMap and add your data set to the new project. Use the Editor tool bar to start the editing process. Make sure that your target is the Rems_junction feature class. From the toolbar use Attributes and select the most downstream junction. Set the AncillaryRole attribute to sink. Save the edits.

Now we will use the Utility Network Analyst to set the flow direction and to do the tracing. 14. Add the Utility Network Analyst tool bar to your user interface. 15. Use the Set Flow Direction tool to create and Flow -> Display Arrows to check the result.

Settings flags, simple tracing can now be done on the network by using the Solve button..

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Task 6: Georeferencing an image and digitizing geometry Up to now we have only used given data sets. If no legacy data is available or no data in the representation (vector or raster) you need, you have to capture it on your own. In the following it is assumed that the banklines of the river Rems are needed in vector representation for further analysis, e.g. as input for a hydrological model. As data only a clipping of a grey color orthophoto is available. Thus we have first to georeference the image and then to digitize the river banks as new line features. For georeferencing, cadastral data (building outlines) are available, which have already coordinates with respect to the DHDN in the Gauss-Krueger-projection zone 3. Image pixels are stored in rows and columns, with the image's origin in the upper left-hand corner. When you add an image to a view, ArcGIS transforms the image coordinates into realworld x and y coordinates. In order to perform this transformation, ArcGIS looks for georeferencing information stored with the image. Some image files (e.g. BIL, BSQ, BIP, GeoTIFF) contain information in their header file. This information can also be stored in a separate ASCII file, a so called world file, because it contains the real-world transformation information used by the image. The world file has a higher priority than a header file, so you can override the transformation in an image's header file by creating your own world file. For other formats, where the header can’t contain any georeferencing information, you have always to store the information in a world file. Here's the content of a typical world file: 12.01 the x-scale (dimension of a pixel in x direction in map units) 0.0 rotation for row 0.0 rotation for column -12.01 the y-scale (dimension of a pixel in y direction in map units, attention: the axis is pointing down!) 128522.92 x coordinate of the center of the upper-left pixel in map units 438509.44 y coordinate of the center of the upper-left pixel in map units An image's world file uses the same name as the image, the first and third characters of the image file's extension, plus a final "w" are used for the world file extension (e.g. *.blw for the BIL format, *.jgw for the JPEG format, *.pgw for PNG format and so on.) The world file has to be located in the same folder as the image file! If there is no information available about location of your image, you have to georeference it manually. Generally, you’ll align your raster to existing spatial data, such as a shape layer, that resides in the desired map coordinate system. This assumes that there are features in your spatial data (target data) that are also visible in the raster - for example, streets, building footprints, and streams. The basic procedure for georeferencing is to move the raster into the same space as the target data by identifying a series of ground control points – of known x,y coordinates - that link locations on the raster with locations in the target data in map coordinates. A combination of one control point on the raster and the corresponding control point on the target data is called a link. The number of links you need to create depends on the method you plan to use to transform the raster to map coordinates. However, adding more links will not necessarily yield a better registration. If possible, you should spread the links out over the entire raster rather than concentrating them in one area. Typically, having at least one link near each corner of the raster and a few throughout the interior produces the best results. In general, the greater the

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overlap between the raster and target data, the better the alignment results because you’ll have more widely spaced points with which to georeference the raster. For example, if your target data only occupies one quarter of the area of your raster, the points you could use to align the raster would be confined to that area of overlap. You can only assume that areas outside the overlap area are properly aligned. To link source and target point, use the georeference tool bar. link table

add control points

When you‘ve created enough links, you can transform – or warp - the raster to map coordinates. Warping uses a mathematical transformation to determine the correct map coordinate location for each cell in the raster. Use a first order - or affine - transformation to shift, scale, and rotate your raster. Straight lines on the raster are mapped onto straight lines in the warped raster. Thus squares and rectangles on the raster are commonly changed into parallelograms of arbitrary scaling and angle orientation. A first-order transformation will probably handle most of your georeferencing requirements. With the minimum of three links, the mathematical equation used with a first-order transformation can exactly map each raster point to the target location. Any more than three links introduces errors, or residuals, that are distributed throughout all the links. In practice, add more than three links. Given only three, if one link is positionally wrong, it has a much greater impact on the transformation. Thus, even though the mathematical transformation error may increase as you create more links; the overall accuracy of the transformation will increase as well. The degree to which the transformation can accurately map all control points can be measured mathematically by comparing the actual location of the map coordinate to the transformed position in the raster. The distance between these two points is known as the residual error. The total error is computed by taking the root mean square (RMS) sum of all the residuals to compute the RMS error. This value describes how consistent the transformation is between the different control points. While the RMS error is a good assessment of the accuracy of the transformation, don’t confuse a low RMS error with an accurate registration. The transformation may still contain significant errors, for example, due to a poorly entered control point. Remark: When you load an image file for the first time, you will be asked if you like to calculate image pyramids. An image pyramid contains the same image in different level on details, i.e. in different resolutions. ArcMap will decide depending on the actual scale which one to load. Thus calculating image pyramids will in general speed up the process of image loading.

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1. The shape-file building.shp contains the footprints of buildings near some part of the river Rems. The tif-file cut7120_78s.tif contains a clip of an orthophoto. The building data is with respect to the datum of the DHDN in Gauss-Krüger projection zone 3. Use ArcCatalog to define the appropriate coordinate system for the shape file. 2. Load both layer to your project in ArcMap. 3. Use the georeferencing tool bar to georeference the orthophoto. Zoom to your vector data such that it fills your map window, than use Fit to Display to shift the orthophoto roughly. Use a symbology for your buildings with helps to identify their outline, e.g. use no fill color and yellow for the outline. 4. Now you have to identify link points, i.e. first click on the photo, second click on the corresponding corner point of the building outline of the vector data. Your RMS should be ca. 1 m for 8 points at least covering the whole photo. Use the link table to check the residuals for the individual points. Points with a very large value are outliers and should be deleted. 5. Use an affine (first order) transformation to warp the photo. Don’t forget to update your georeferencing: two files (*.aux and *.tfw will be written with the georeferencing information).

ArcCatalog lets you create new shapefiles and dBASE tables and modify them by adding, deleting, and indexing attributes. You can also define a shapefile’s coordinate system and update its spatial index. While you can change the structure and properties of a shapefile in ArcCatalog, you must use ArcMap to modify its features and attributes - for example, to add values into a new column by performing a calculation on values in another column. So we will use ArcCatalog to create a new empty shapefile to store our river bank lines. 1. Start ArcCatalog and browse to the folder where your project shapefiles are located. Right click the folder name and select New -> Shapefile from the menu. 2. In the dialog, enter a name for your new shapefile layer and make sure that the feature type Polyline is selected. Change the setting for the coordinate system to DHDN zone 3. 3. Change to the table view in ArcCatalog and add the fields to your shapefile you need to store the attributive data. Make sure to use the appropriate data types. Here we want to store the river name and the location of the bank line with respect to the river, i.e. left or right. 4. Add your new created shapefile as a new layer to your map in ArcMap. 5. Start your editing session from the Edit toolbar. Select the task (Create New Feature) for your target (i.e. the layer, you have just created). 6. Add the vertexes to the layer by clicking the left mouse button in the map. Make sure that every start point of a new line exactly snaps on the end point of the previous line (use the snapping settings you find in the Options of the Editor tool bar) 7. Open the attribute table and enter values into the fields for each line by using the Edit tool. 8. Don’t forget to stop the edit session to save your changes.

Prof. Dr. D. Schröder Page 18

GIS in Hydrology and Water Management - ENWAT

Task 7: Determine areal precipitation by the Thiessen method Areal precipitation is frequently estimated by a weighted mean of measured precipitation at rain gauges in and near the watershed. As input for hydrological models, often Thiessen polygons are needed, which assigns the value of the closest observation point to each point in the domain. In this tutorial Thiessen polygons will be created for calculating the average annual rainfall for the whole Rems watershed. As input data, the locations shape file (cities and other settlement locations) and a text file with rainfall data will be used (precipitation.tab). The text file contains the name of the station, the precipitation for each month, and the summed up yearly precipitation. The columns are separated by a tab. 1. Load the two files and join them using the common field, i.e. the names of the locations. Use the Advanced button to keep only those rows which have a match in the other table (28 locations) 2. Export the joined result to a new shape file and add it to your project. 3. Create the Thiessen polygons based on the file from step 2. Use the option Output Field ALL to get the point attributes to the polygons. (Remark: this only will work on “real” attributes, not on joined ones. For that step 2 was necessary.)

Prof. Dr. D. Schröder Page 19

GIS in Hydrology and Water Management - ENWAT

Now we want to assign weights to the Thiessen polygons according to their share in the Rems watershed. First we have to restrict the polygons area to that of the watershed. 4. Use Clip to restrict the polygons to the watershed area. Use the Rems watershed shapefile as clipping layer.

Next we have to do some calculations on the attributes. We need the share of each Thiessen polygon on the whole watershed. We will use VBA for defining the complex calculation. 5. Determine the size of the watershed using the Measurement tool (hint: to be sure to select the correct feature, turn off all the other layers.) 6. Add a new field to the attribute table of your Thiessen polygons called share with data type double. 7. Populate the field using the Field calculator using the formula Dim Output as double Dim pArea as Iarea Set pArea = [shape] Output = [sum] * pArea.area/583117904

For calculating the average annual rainfall for the whole watershed, we can use the statistics for our new column.

Prof. Dr. D. Schröder Page 20

GIS in Hydrology and Water Management - ENWAT

Task 8: Determine areal precipitation by Grid interpolation

Another possibility to the calculation of the average annual rainfall is to uses raster tools. Here we have first to interpolate the sparse data from the climate stations to a dense raster. Than the raster values can be summed up considering the size of each pixel. 1. Load the shape file with the location and their precipitation data you have created in the preceding tutorial. 2. Activate the Spatial Analyst Extension and add its toolbar to your GUI. 3. Interpolate the location to a raster. Make sure to use the sum of precipitation as Z value field. Try the IDW and the Spline interpolation with different settings for the parameters. Use a reasonable cell size for your raster. (Remark: a temporarily created raster will be stored when you exit ArcMap (but in the default folder!), you can make it permanently by exporting it to a grid.

As we are only interested in the cells inside the watershed, we have to clip the result again. Clipping of a raster, i.e. extracting the raster cells covered by another layer is called masking. 4. Use the Mask tool from the Spatial Analyst Tools of the ArcToolbox. As input raster, use your final interpolation, as feature mask data the Rems watershed layer. Check the folder for saving the result raster. 5. As the result of the interpolation was a floating point layer, we have no VAT associated with the raster that means we can not perform any calculations based on attributes. So we have to convert it to an integer layer using the raster calculator 6. In the VAT we have one row entry for each class, i.e. cells with the same value. Each row includes the value and the number of pixels with this value. To calculate the average annual rainfall, we have just to multiply the values with their number of occurrence, some them up and divide the result by the total number of cells. Use the Zonal statistic tool to get the sum, i.e. the number of cells times their values. 7. With the statistics of the column sum you get the summed up cell values, use a calculator to divide it by the total number of cells (i.e. the sum of the column count) 8. Compare the result with the result you got from the Thiessen polygon method.

Prof. Dr. D. Schröder Page 21

GIS in Hydrology and Water Management - ENWAT